In the last twenty years, computers have played an ever-increasing role in the airline industry. For example, computers are used onboard an aircraft for such tasks as aiding navigation, scheduling maintenance, and monitoring the operation of equipment, as well as for controlling the position of the flight control surfaces to fly the aircraft. On the ground, computers are used to ticket passengers, keep track of their luggage, maintain records of seat availability, and schedule departure changes. Despite recent advances in computer network system technology, the ability to exchange data between the aircraft computer system and the ground-based computer system used by an airline has remained limited. What information transfer does take place is typically accomplished by hand carrying computer discs between the two computer systems. Due to the desirability of transmitting information between an aircraft computer system and a ground-based computer, there has been a considerable research effort within the aircraft industry to develop an aircraft to ground-based computer communications link.
One new communications system for transmitting information between an aircraft computer system and a ground-based computer system is disclosed in commonly assigned U.S. patent application Ser. No. 07/943,328, filed Sept. 10, 1992, the specification of which is herein incorporated by reference. This system discloses a free-space optical communications link that transmits data between an aircraft computer system and a ground-based computer system using an infrared light beam. An optical transceiver disposed below a passenger door of the aircraft transmits a modulated infrared beam to a corresponding optical transceiver that is located on a passenger loading bridge. Both the transceiver on the passenger bridge and on the aircraft include a separate optical transmitter and receiver for transmitting and receiving infrared optical signals that correspond to the data transmitted between the two computer systems. When the aircraft is docked at the passenger loading bridge, the optical transceiver on the aircraft is aligned with the corresponding optical transceiver such that information transfer can take place by transmitting the infrared beams through the air space that exists between the two transceivers.
While the above-referenced system works well to transmit data between the aircraft computer system and the ground-based computer system, there are some situations in which it is either impossible or impractical to provide an optical transceiver in close proximity with the optical transceiver disposed on the aircraft so that information can be transmitted between the two computer systems. For example, in certain airports, passengers do not board aircraft in the type of loading bridge upon which it is convenient to mount the optical transceiver, as described in the referenced patent application. Some airports use movable stairs disposed on motorized vehicles to board the passengers while others rely on stairs that are built into the aircraft to board the passengers. In either case it would be difficult to mount an optical transceiver in close proximity with the optical transceiver disposed on the aircraft so that data communication can take place. In the case where movable stairs are used, an optical transceiver would have to be mounted on the stairs and some type of cable would need to run to a manhole or some other location to carry the data to the ground-based computer. However, because such vehicles are movable, the possibility exists that the vehicle with the stairs attached would drive off and break the cable or that the vehicle would not be at its proper location when the aircraft docked, thereby delaying the linking of the two computer systems. In the case where passengers board the aircraft using a built-in stairway, an adjustable scaffold would have to be provided to align the optical transducers. Such a scaffold would most likely be cumbersome, interfere with the ground crew's access to the aircraft and get in the way when not in use.
Another situation where it is not practical to provide an optical transceiver that can be placed in close proximity with the optical transceiver disposed on the exterior of the aircraft is when the aircraft is parked at some remote location in an airport such as a holding area or in a repair hangar. Such a location would also have to be equipped with a scaffold that could align the optical transceiver with the transceiver on the aircraft. Again, such a scaffold would most likely be cumbersome and would interfere with the ground crew's access to the aircraft.
Therefore, a need exists for a communications system that can transmit information between an aircraft computer system and a ground-based computer system in those situations where it is either not feasible or not practical to provide an adjustable mechanism for aligning an optical transceiver to transmit and receive infrared signals from the optical transceiver disposed on the exterior of the aircraft. The system should be rugged and able to work in extreme environments. Most importantly, the system should be compatible with the existing aircraft infrared communications system referenced above.